“This is what it is like being in control, you have the ultimate ­decision about whether you live or die in a peaceful and reliable way,” Nitschke said. That, in a nutshell, is the right he campaigns for.

It’s a right people such as locked-in syndrome sufferer Tony ­Nicklinson – who ultimately ended his life by refusing food – have fought for through the courts. But deliberately assisting or ­encouraging another person to kill themselves remains illegal and punishable by up to 14 years in prison.

What Nitschke does is right on the edge. Last week, he was to showcase Destiny in Edinburgh Fringe show Dicing with Dr Death, until the police and council stepped in and banned him from using the canisters of nitrogen in the show.

He went ahead without the gas and claims he will sell the machine online, insisting it will be legal.

“Destiny doesn’t use illegal substances. It doesn’t depend on the use of a prohibited substance…If a person sells you a rope and you go home and hang yourself is the person who sells it responsible for your suicide?

But this has been designed for suicide,” he said. “So it maybe is on the edge of the law… but it will be harder to outlaw.” Nitschke, 67, says he would sell Destiny for “a few hundred dollars” and many claim he exploits the vulnerable – but he says Exit is non-profit making.

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Some who come to Exit are terminally ill – a scenario which will be debated in the Commons in next month. But most people approach Exit because they want to know faced with illness, they will be able to slip away.

Others, simply don’t want to go on for reasons ranging from ­quadriplegia to depression to the fact their partner is dying and they “want to go with them”.

As long as it’s “rational suicide”, Nitschke argues, they’re of sound mind, and they’re over 50, he will “signpost” them.

Although, ­horrifyingly, he admits, he will consider anyone over 18 if their reason is valid.

Nitschke, and his team of volunteers, including his wife Fiona Stewart, 48, decide who is “rational”. For many, that just doesn’t wash.

“His views are opposed by every major doctors’ group and disability rights organisation in Britain,” said Dr Peter Saunders of Care Not Killing. “The Royal College of ­Psychiatrists have said clearly those suffering from mental health ­problems need care not access to a lethal cocktail of drugs.”